Field of the Invention
The present disclosure relates to copolymers, coloring material dispersions, inks and ink stored containers.
Description of the Related Art
Compared with other printing methods, inkjet printing methods have simple processes, can be easily accommodated to full-color operations, and can provide high-resolution images even when used on apparatuses having simple configurations. Therefore, the inkjet printing methods are spreading to personal and office use and commercial printing and industrial printing fields.
In the inkjet printing methods, aqueous ink compositions using aqueous dyes as coloring materials have been used. The aqueous ink compositions however have a problem that the aqueous ink composition using the aqueous dye lacks in water resistance and lightfastness. Accordingly, pigment inks using water-insoluble pigments replacing the aqueous dyes have been developed.
When the pigment ink is printed on plain paper, the pigment penetrates into the paper without being remained on a surface of the paper, and therefore a density of the pigment on the surface of the paper is low, leading to a low image density. The image density increases, if a concentration of the pigment in the ink increases. However, the ink having a high pigment concentration has problems that a viscosity of the ink increases to deteriorate ejection stability.
To solve the above-described problems, for example, proposed is an inkjet ink including a liquid vehicle, a coloring material, and a polymer including at least one functional group having a certain calcium index value (see, e.g., Japanese Patent No. 5001291).
When an image having excellent resolution and vividness on various print media, especially media having low permeability or nonpermeable films, such as coated paper and art paper, moreover, there is a problem that beading (unevenness) tends to occur.
In order to solve the above-described problem, for example, proposed is a method where rheology is an ink is changed with a change of pH using a pH-responsive polymer including a plurality of hydrophilic segments arranged at side chains, and a plurality of pH-responsive segments which change between hydrophilic nature and hydrophobic nature depending on a value of pH (see, e.g., Japanese Unexamined Patent Application Publication No. 2012-52027).
Moreover, aqueous pigment inks used for the inkjet printing method and for writing instruments are different from aqueous dye inks each prepared by dissolving a dye in water, and the pigments, which are insoluble in water, in the aqueous pigment inks need to be stably dispersed in water over a long period. Therefore, various pigment dispersing agents have been developed.
For example, proposed as a pigment dispersing agent is a graft polymer including an aromatic ring at a side chain (see, e.g., Japanese Unexamined Patent Application Publication No. 2011-105866).